全文获取类型
收费全文 | 7055篇 |
免费 | 1110篇 |
国内免费 | 1013篇 |
专业分类
化学 | 5560篇 |
晶体学 | 113篇 |
力学 | 416篇 |
综合类 | 49篇 |
数学 | 860篇 |
物理学 | 2180篇 |
出版年
2024年 | 24篇 |
2023年 | 128篇 |
2022年 | 189篇 |
2021年 | 256篇 |
2020年 | 327篇 |
2019年 | 339篇 |
2018年 | 282篇 |
2017年 | 243篇 |
2016年 | 393篇 |
2015年 | 376篇 |
2014年 | 431篇 |
2013年 | 586篇 |
2012年 | 613篇 |
2011年 | 687篇 |
2010年 | 475篇 |
2009年 | 437篇 |
2008年 | 455篇 |
2007年 | 378篇 |
2006年 | 366篇 |
2005年 | 292篇 |
2004年 | 277篇 |
2003年 | 211篇 |
2002年 | 249篇 |
2001年 | 190篇 |
2000年 | 129篇 |
1999年 | 130篇 |
1998年 | 78篇 |
1997年 | 76篇 |
1996年 | 61篇 |
1995年 | 49篇 |
1994年 | 59篇 |
1993年 | 34篇 |
1992年 | 31篇 |
1991年 | 36篇 |
1990年 | 36篇 |
1989年 | 27篇 |
1988年 | 32篇 |
1987年 | 14篇 |
1986年 | 19篇 |
1985年 | 23篇 |
1984年 | 10篇 |
1983年 | 12篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1975年 | 8篇 |
1974年 | 6篇 |
排序方式: 共有9178条查询结果,搜索用时 15 毫秒
101.
Chen H Aleksandrov A Chen Y Zha S Liu M Orlando TM 《The journal of physical chemistry. B》2005,109(22):11257-11262
Polycrystalline gadolinia-doped ceria (GDC) surfaces were studied using low-energy (5-400 eV) electron stimulated desorption (ESD). H(+), O(+), and H(3)O(+) were the primary cationic desorption products with H(+) as the dominant channel. H(+), H(3)O(+), and O(+) have a 22 eV threshold followed by a yield change around 40 eV. H(+) also has an additional yield change approximately 75 eV and O(+) has an additional change approximately 150 eV. The O(+) ESD yield change approximately 150 eV may indicate bond breaking of Gd-O and the involvement of oxygen vacancies. The H(+) and H(3)O(+) threshold data collectively indicate the presence of hydroxyl groups and chemisorbed water molecules on the GDC surfaces. ESD temperature dependence measurements show that the interaction of water with GDC surface defect sites, mainly oxygen vacancies, influences the desorption of H(+), O(+), and H(3)O(+). The temperature dependence of the O(+) ESD at 400 eV incident electron energy yields a 0.21 eV activation energy. This is close to the energy needed for oxygen vacancy production next to a pair of Ce(3+) on a CeO(2) surface. These results may indicate a correlation between the O(+) ESD yield and oxygen vacancy density on GDC surfaces and a potential correlation of O(+) ESD and GDC ionic conductivity. 相似文献
102.
Xiao Long WANG Jian Peng FENG Xin Gang XIE Xiao Ping CAO* Xin Fu PAN* Department of Chemistry & State Key Laboratory of Applied Organic Chemistry Lanzhou University Lanzhou 《中国化学快报》2004,(9)
Aiphanol was isolated from the seeds of Aiphanes aculeate Willd. (Arecaceae) collected in Peru and was reported to exhibit significant inhibitory activities against cyclooxyge- nases-1 and -2. The structure of aiphanol was elucidated by spectroscopic methods as an unprecedented stilbenolignan skeleton in which a stilbene moiety is linked to a phenylpropane unit through a dioxane bridge1. In our previous works the synthetic approach to 1,4-benzodioxane lignans were achieved2. Since aiphanol… 相似文献
103.
Zhanglin Liu Dong Tian Fei Shen Lulu Long Yanzong Zhang Gang Yang Yongmei Zeng Jing Zhang Jinsong He Ying Zhu Shihuai Deng 《中国化学快报》1990,30(12):2221-2224
Four distinct biochars were employed to remove three typical pollutants, meanwhile, path analysis, a multi-statistical regression method, was performed to elucidate the dominant factors of biochar adsorption. This work can provide a new insight to prepare a targeted biochar as adsorbents. 相似文献
104.
105.
Timothy B. Hutson Ming J. W. Chang Joseph T. Keller David J. Long 《Mikrochimica acta》1988,94(1-6):339-341
Fourier transform infrared techniques were used to monitor mammalian cell growth plated on attenuated total reflection (ATR) crystals. Consistently, the growth kinetics plots generated from the obtained spectra demonstrated a sigmoidal curve representing a sequence of slow, rapid, then tapering cell growth which correlated well with non-spectral cell growth determinations. Significant advantages over traditional methods of measuring cell growth kinetics are demonstrated. The technique has promising potential to be used to study events in areas such as toxicology and cell biology. 相似文献
106.
三溴偶氮胂催化光度法测定痕量铁 总被引:19,自引:2,他引:19
本文研究了硫酸介质中痕量 Fe(Ⅲ)催化加速抗坏血酸、溴酸钾和三溴偶氮胂之间的褪色反应及动力学条件,建立了动力学光度法测定痕量Fe(Ⅲ)的新方法.方法灵敏度为1.82×10~(-12)g·ml~(-1).测定范围为Fe(Ⅲ)0~30ng/25ml.已用于人发和食品中痕量铁的测定.结果满意. 相似文献
107.
合成了3个新型开链冠醚Schiff碱-稀土离子三元配合物RE(H2L)(Mq)(NO3)3,其中RE=Nd3 ,Er3 ,Yb3 ,配体H2L=N,N-双(邻羟苯亚甲基)-3,6-二氧杂-1,8-二氨基辛烷,Mq为8-羟基喹哪啶.采用元素分析、红外光谱(IR)、紫外-可见吸收光谱(UV-vis)、热重-差热分析(TG-DTG)等手段对配合物的组成结构进行了表征.测定了3种新型结构稀土三元配合物在不同温度(77 K和300 K)时的近红外发光光谱. 相似文献
108.
109.
Preparation,stability and two-dimensional ordered arrangement of gold nanoparticles capped by surfactants with different chain lengths 总被引:2,自引:0,他引:2
Gold nanoparticles modified with C10NH2, C12NH2, C16NH2 and C18NH2 respectively have been prepared by the reverse micelle method. Nanoparticles stability and their two-dimensional (2D) ordered arrangement were studied by UV-Vis absorption spectra and LB technique. The factors, such as the chain length and the size distribution of particles, which affect the 2D ordered arrangement formation, are discussed. Experimental results show that the longer the chain length of surfactants capping the gold nanoparticles, the more stable the nanoparticles, and the more ordered 2D arrangement of gold nanoparticles. 相似文献
110.
不饱和链烃沸点的拓扑研究 总被引:4,自引:0,他引:4
基于邻接矩阵与边价 (fi)定义边价连接性指数 ( mF) ,其中的0 F ,1 F与 2 94种不饱和链烃 (包括烯烃、炔烃及烯炔烃 )的沸点 (Tb)关联 ,得到良好的数学模型 :ln( 70 0 -Tb) =6 5 2 3 3 1-0 0 0 4880 F2 -0 3 46771 F0 5(n =2 94,R =0 9979,R2 =0 995 8,F =3 490 4,S =5 12 ) ,该回归模型经Jackknife法检验具有总体稳健性 .可以预示 ,该指数将在定量构效关系研究中成为重要参数 . 相似文献